Rotor and process for manufacturing the same

ABSTRACT

A rotor comprising bonded magnet portions mainly composed of magnet powder and a binder, which are embedded in a soft magnetic portion mainly composed of soft magnetic powder and a binder, the rotor being produced by a compression-molding method, and the magnetic pole surfaces of the bonded magnet portions being embedded in the soft magnetic portion.

FIELD OF THE INVENTION

The present invention relates to a rotor integrally comprising permanentmagnets and a yoke suitable for high-efficiency motors, generators, etc.

BACKGROUND OF THE INVENTION

As permanent magnet motors, there are surface permanent magnet (SPM)motors comprising permanent magnets on peripheral portions of rotors,and interior permanent magnet (IPM) motors comprising permanent magnetsembedded in rotors, etc.

As shown in FIG. 16, the SPM motor has a structure in which permanentmagnets 31 on a rotor surface are in direct contact with an air gap 34between the rotor and a stator 33 comprising a yoke 32 and coils 37. Themagnetic circuit shown in FIG. 16 is generally called asurface-magnet-type magnetic circuit. A magnetic flux A₁ emanating froman N pole of a permanent magnet 31 a penetrates the air gap 34, passesthrough portions 33 a, 33 b and 33 c of the stator yoke 33, andpenetrates the air gap 34 again, passes through a permanent magnet 31 band the rotor yoke 32, and returns to an S pole of the permanent magnet31 a, as shown by the arrow.

As shown in FIG. 17, the magnetic circuit of the IPM motor is called amagnet-embedded magnetic circuit or an interior-magnet-type magneticcircuit because permanent magnets 41 are embedded in a yoke 42. The yoke42 is formed by a laminate of silicon steel sheets punched out to havemagnet-shaped holes, and permanent magnets 41 are received in the holesof the yoke 42. A magnetic flux A₄ emanating from an N pole of apermanent magnet 41 passes through the rotor yoke 42, penetrates an airgap 44 between a stator 43 and a rotor, successively passes throughportions 43 a, 43 b, 43 c of a stator yoke, penetrates the air gap 44again, passes through the rotor yoke 42, and returns to an S pole of thepermanent magnet 41, as shown by the arrow.

Both B₁ and B₂ in FIGS. 16 and 17 denote short-circuited magneticfluxes. The magnetic fluxes B₁, B₂ do not act on the stator, resultingin no contribution to a torque. The magnetic fluxes B₁, B₂ areundesirable because they eat the magnetic flux contributing to thetorque of a motor.

Many proposals were made to provide reluctance motors utilizing thesaliency of soft magnetic portions in magnet rotors for a reluctanceeffect as shown by A₅ in FIG. 17 (see Sakai, et. al., “BasicCharacteristics of Permanent Magnet Reluctance Motor,” at the 1998Meeting of the Japan Electricity Association, Lecture No. 1002). Thereluctance motors are classified to switched reluctance motors andsynchronous reluctance motors by stator surfaces. The switchedreluctance motor generally comprises a stator having concentratedwindings, and a gear-shaped rotor magnetically attracted to the teeth ofthe stator for rotation. The synchronous reluctance motor generallycomprises a stator having distributed windings, and a rotor having oneor more magnetic barriers therein. The magnetic barriers form a d-axisthrough which a magnetic flux easily flows, and a q-axis through which amagnetic flux does not easily flow, the difference in inductance betweenboth axes generating reluctance torque.

Permanent magnets have drastically smaller specific permeabilities thanthose of soft magnetic materials such as silicon steel, etc. Utilizingthe difference in specific permeability between permanent magnets andsoft magnetic materials, motors having both characteristics of thepermanent magnet motors and the reluctance motors can be achieved. AsIPM motors, too, motors using permanent magnets as magnetic barriers togenerate reluctance torque, thereby having both characteristics of thepermanent magnet motors and the reluctance motors, can be achieved.Particularly because the magnet-embedded motors can effectively utilizemagnetic fluxes generated by permanent magnets, they have improvedefficiency at a low-speed rotation. They can also rotate up to ahigh-speed zone by utilizing a by-produced reluctance torque.

Magnet-embedded motors such as synchronous reluctance motors are called“reluctance permanent magnet (RPM) motors,” utilizing mainly a magnettorque and auxiliarily a reluctance torque. See W. L. Soong, T. J. E.Miller: “Practical Field-Weakening Performance of the Five Classes ofBrushless Synchronous AC Motor Drive,” Proceedings of European PowerElectronics Conference (1993), and W. L. Soong, D. A. Stanton, T. J. E.Miller: “Design of New Axially-Laminated Permanent Magnet Motor,”Proceedings of IEEE Industry Applications Society Annual Meeting (1993).

Such drastic improvement of the characteristics of permanent magnetsprovides motors with intermediate characteristics between the permanentmagnet motors and the reluctance motors. Among them, permanentmagnet-embedded motors are promising, because they have high efficiencyand high-accuracy control, and because they can be provided withoptimized characteristics for motor applications.

On the other hand, in motors widely used at present, thin plates such assilicon steel sheets, etc. having openings for permanent magnets arelaminated, and constituent members are small. Accordingly, such motorsare not suitable for high-speed rotation. In addition, because permanentmagnets inserted into the above openings are adhered, clearance isneeded to absorb working tolerance between the permanent magnets and thesilicon steel sheets. This clearance acts as an air gap in a magneticcircuit, thereby lowering the efficiency of motors. Further, theclearance deteriorates the positional accuracy of the permanent magnets,resulting in uneven magnetic pole pitches and thus a cogging torque.

In addition, to lower a production cost, it is necessary to provide thepermanent magnets and the silicon steel sheets with simple shapes,thereby simplifying their working. Accordingly, it is difficult toproduce extremely thin portions of the permanent magnets and the siliconsteel sheets with high accuracy. To effectively use a reluctance torque,however, there is an increasingly higher demand to provide irregularlyshaped magnets. To solve such problems, JP 7-169633 A proposes a methodfor integrally molding permanent magnets and a soft magnetic material.However, this method is applicable only to the SPM motors, failing tosolve the production problems of the magnet-embedded motors.

A magnet-embedded rotor needs bridging soft magnetic portions foravoiding impact and for reinforcement between pluralities of permanentmagnets, but these portions permit the short-circuiting of a magneticflux generated by the permanent magnets, resulting in a leaked magneticflux. Accordingly, the magnetic generated by the permanent magnetscannot be fully used. To solve such problems, JP 8-331784 A proposes theconstruction of a yoke by a member having both magnetic portions andnon-magnetic portions, and the formation of non-magnetic portions in thebridging portions. However, this technology fails to solve the aboveproblems in working or production.

When magnet powder and soft magnetic powder are integrallycompression-molded, a compression-molded body is subjected to crackingby springback at the time of removing it from a die. Even if no crackingoccurred, a rotor assembled in a motor would likely be cracked by acentrifugal force if there were a weak press-bonding strength betweenthe magnetic portions and the non-magnetic portions.

JP 2002-134311 A proposes a method for forming bonded magnets in a rotorwithout clearance by laminating thin plates such as silicon steelsheets, etc. having openings for receiving magnets, and injecting acompound for the bonded magnets into the openings. However, because thecompound should contain a large amount of a resin (a small amount ofmagnet powder or iron powder) to have high flowability in this method,the resultant rotor suffers low magnetic characteristics. In addition,the larger the motor is, the more current flows in permanent magnets,resulting in an increased eddy current loss. To reduce the eddy currentloss, Mita, “Eddy Current Analysis of Surface Magnet Motor,” '98 MotorTechnology Symposium (1998) describes that a pole of each magnet shouldbe divided, and that the flow of electric current should be cut bysurface coatings or bonding layers. However, this method needs a lot ofsteps, resulting in a high production cost.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide apermanent magnet-embedded rotor free from gaps between permanent magnetsand a soft magnetic material and cracking due to springback, capable ofeffectively utilizing a magnetic force generated by permanent magnetsbecause of a high degree of freedom in their shapes, and having highpress-bonding strength between bonded magnet portions and a softmagnetic portion.

Another object of the present invention is to provide a method forproducing such a permanent magnet-embedded rotor.

DISCLOSURE OF THE INVENTION

Thus, the rotor of the present invention comprises a soft magneticportion mainly composed of soft magnetic powder and a binder, and bondedmagnet portions mainly composed of magnet powder and a binder andembedded in the soft magnetic portion, the rotor being formed by acompression-molding method, and the magnetic pole surfaces of the bondedmagnet portions being substantially embedded in the soft magneticportion.

In one embodiment of the present invention, the end surfaces of thebonded magnet portions are exposed on a peripheral side surface of therotor, the width of each exposed end surface having being 2% or less ofthe entire periphery of the rotor. In another embodiment of the presentinvention, the bonded magnet portions are totally embedded in the softmagnetic portion, the thinnest portion of the soft magnetic portionbetween the bonded magnet portions and the peripheral side surface ofthe rotor having a thickness of 0.3-1.5 mm.

The bonded magnet portions each having a circular shape curved toward acenter of the rotor are preferably arranged such that the rotor hasmagnetic poles in an even number of 4-12. The arcuate bonded magnetportions are preferably circularly connected.

The magnet powder preferably has an average particle size of 50-200 μm,and the soft magnetic powder preferably has an average particle size of1-50 μm.

The soft magnetic portion preferably has electric conductivity of 20kS/m or less, Bm of 1.4 T or more, and coercivity Hc of 800 A/m or less.The bonded magnet portions preferably have a residual magnetic fluxdensity Br of 0.4 T or more and Hcj of 600 kA/m or more. A shearstrength between the bonded magnet portions and the soft magneticportion is preferably 10 MPa or more.

The first method of the present invention for producing a rotorcomprising bonded magnet portions and a soft magnetic portion comprisespreliminarily molding the bonded magnet portions from a magnet powdercompound mainly composed of magnet powder having an average particlesize of 50-200 μm and a binder; preliminarily molding the soft magneticportion from a soft magnetic powder compound mainly composed of softmagnetic powder having an average particle size in a range of 1-50 μm,and a binder, such that the soft magnetic portion is in contact with thebonded magnet portions; and making the bonded magnet portions and thesoft magnetic portion integral at a higher pressure than a preliminarymolding pressure.

The second method of the present invention for producing a rotorcomprising bonded magnet portions and a soft magnetic portion comprisespreliminarily molding (a) the bonded magnet portions from a magnetpowder compound mainly composed of magnet powder having an averageparticle size of 50-200 μm and a binder, and (b) the soft magneticportion from a soft magnetic powder compound mainly composed of softmagnetic powder having an average particle size in a range of 1-50 μm,and a binder, separately; assembling the bonded magnet portions and thesoft magnetic portion; and making them integral at a higher pressurethan a preliminary molding pressure.

The third method of the present invention for producing a rotorcomprising bonded magnet portions and a soft magnetic portion comprisespreliminarily molding the soft magnetic portion from a soft magneticpowder compound mainly composed of soft magnetic powder having anaverage particle size in a range of 1-50 μm, and a binder; preliminarilymolding the bonded magnet portions from a magnet powder compound mainlycomposed of magnet powder having an average particle size of 50-200 μmand a binder, such that the bonded magnet portions are in contact withthe soft magnetic portion; and making the soft magnetic portion and thebonded magnet portions integral at a higher pressure than thepreliminary molding pressure.

In any methods for producing a rotor, it is preferable to use athermosetting resin as the binder, and to conduct a thermosettingtreatment after the bonded magnet portions and the soft magnetic portionare made integral.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to one embodiment of the presentinvention;

FIG. 1( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 1( a) when it wasdeformed;

FIG. 2( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to another embodiment of the presentinvention;

FIG. 2( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 2( a) when it wasdeformed;

FIG. 3( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a further embodiment of the presentinvention;

FIG. 3( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 3( a) when it wasdeformed;

FIG. 4( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 4( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 4( a) when it wasdeformed;

FIG. 5( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor having each magnetic pole provided by pluralitiesof bent bonded magnet portions;

FIG. 5( b) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor having each magnetic pole provided by pluralitiesof arcuate bonded magnet portions;

FIG. 6( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 6( b) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 6( c) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 6( d) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 6( e) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 7( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 7( b) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor according to a still further embodiment of thepresent invention;

FIG. 8( a) is a partial cross-sectional view showing an apparatus forcompression-molding the permanent magnet-embedded rotor of the presentinvention;

FIG. 8( b) is a perspective view showing an upper punch assembly in thecompression-molding apparatus shown in FIG. 8( a);

FIG. 8( c) is a perspective view showing the upper punch assembly ofFIG. 8( b), which is disassembled to upper punches for molding bondingparts and upper punches for molding soft magnetic portions;

FIG. 9 is a transverse cross-sectional view showing thecompression-molding steps of the permanent magnet-embedded rotor of thepresent invention using the apparatus of FIG. 8( a);

FIG. 10( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor in Comparative Example 1;

FIG. 10( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 10( a) when it wasdeformed;

FIG. 11 is a graph showing the relation between an exposure ratio of theend surfaces of a bonded magnet portion and a residual stress at the endsurface;

FIG. 12( a) is a schematic cross-sectional view showing a permanentmagnet-embedded rotor in Comparative Example 2;

FIG. 12( b) is a schematic view showing a tensile stress distribution inthe permanent magnet-embedded rotor shown in FIG. 12( a) when it wasdeformed;

FIG. 13 is a graph showing the relation between the thickness of thethinnest portion of a soft magnetic portion and a residual stress there;

FIG. 14 is a cross-sectional view showing a rotating machine comprisingthe permanent magnet-embedded rotor of Example 1;

FIG. 15 is a graph showing the relation between a torque (normalized)generated by the rotating machine of Example 6 and an electrical angle;

FIG. 16 is a cross-sectional view showing a conventional surfacepermanent magnet (SPM) motor; and

FIG. 17 is a cross-sectional view showing a conventional interiorpermanent magnet (IPM) motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[1] Rotor

[A] Composition

(1) Powder

Though not particularly restricted, the magnet powder are preferably,for instance, Sm—Co magnet powder comprising as basic components a rareearth element (mainly Sm) and a transition metal (mainly Co); R-T-Bmagnet powder comprising R (at least one of rare earth elementsincluding Y), T (transition metal, mainly Fe) and B as basic components;R-T-N magnet powder comprising a rare earth element (mainly Sm), T(transition metal, mainly Fe) and N as basic components; or thesemixtures. The magnet powder may be either isotropic or anisotropic.Because a magnetic flux is shorted-circuited in a permanentmagnet-embedded rotor, a sufficient magnetic flux cannot be obtained ona rotor surface, when a residual magnetic flux density Br is less than0.4 T as in bonded ferrite magnets, for instance. Accordingly, it ispreferable to use bonded rare earth magnets having Br≧0.4 T, andcoercivity Hcj≧600 kA/m.

The soft magnetic powder is preferably atomized iron powder, Fe—Copowder, Fe-based, nanocrystalline magnetic powder, etc. The softmagnetic powder preferably has electric conductivity of 20 kS/m or less,Bm of 1.4 T or more, and Hc of 800 A/m or less. When the electricconductivity is 20 kS/m or less, eddy current loss can be reduced tosubstantially the same level as insulated laminates of silicon steelsheets. When Bm is less than 1.4 T, a sufficient magnetic flux cannot beobtained. When Hc is more than 800 A/m, there is a remarkable hysteresisloss during the rotation of a motor, resulting in a motor with extremelylow efficiency.

The magnet powder preferably has an average particle size of 50-200 μm,and the soft magnetic powder preferably has an average particle size of1-50 μm, smaller than that of the magnet powder. Because of differencein particle size between the magnet powder and the soft magnetic powder,bonded magnet portions and soft magnetic portions have high bondingstrength, thereby suppressing cracking. The more preferred averageparticle size is 80-150 μm for the magnet powder, and 5-30 μm for thesoft magnetic powder.

The magnet powder and the soft magnetic powder are preferably providedwith an insulating coating, to increase electric resistance and reducean eddy current loss during the rotation of a motor.

(2) Binder

Binders are preferably thermosetting resins such as epoxy resins, phenolresins, urea resins, melamine resins, thermosetting polyester resins,etc. The amount of the binder is preferably 1-5 parts by mass, morepreferably 1-4 parts by mass, per 100 parts by mass of the magnetpowder. It is also preferably 0.1-3 parts by mass, more preferably 0.5-2parts by mass, per 100 parts by mass of the soft magnetic powder. A toosmall amount of the binder provides a rotor with extremely lowmechanical strength. On the other hand, a too much amount of the binderprovides a rotor with extremely low magnetic characteristics.

[B] Structure

An IPM rotor utilizing a reluctance torque can generate a larger motoroutput than an SPM rotor. However, the use of a reluctance torquesubjects a rotor yoke to an excessive alternating magnetic field,resulting in a remarkable eddy current loss. To avoid the eddy currentloss, it is necessary to extremely reduce electric conductivity in anintegrally molded rotor comprising bonded magnet portions and softmagnetic portions. Accordingly, the rotor of the present inventionshould have a peripheral side surface covered by a thin soft magneticportion. In this case, the soft magnetic portion preferably has electricconductivity of 20 kS/m or less.

To prevent the short-circuiting of a magnetic flux, the IPM rotorpreferably has thin soft magnetic portions between the bonded magnetportions and a peripheral side surface. In a rotor having such astructure that magnets are inserted into openings in the soft magneticportions constituted by silicon steel sheets, etc., portions of thesilicon steel sheets between the magnets and the peripheral side surfacecannot be made very thin to secure mechanical strength. On the otherhand, in the rotor of the present invention having such a structure thatbonded magnet portions and soft magnetic portions are integrally molded,there is a large degree of freedom in the design of thin portions,resulting in less restriction in the thickness of the thin portions.Specifically, the thinnest portions in the soft magnetic portionsbetween the outer surfaces of the bonded magnet portions and theperipheral side surface of the rotor preferably have a thickness in arange of 0.3-1.5 mm.

(1) Embodiments

FIG. 1( a) shows a permanent magnet-embedded rotor according to oneembodiment of the present invention. In the rotor in this embodiment,arcuate bonded magnet portions 1 each having a thicker center portion 1b than an end 1 a are embedded in soft magnetic portions 2, and the ends1 a, 1 a of adjacent bonded magnet portions 1, 1 are separated such thatthere is no short-circuiting of a magnetic flux between magnetic poles.Each end surface 1 c is exposed on a peripheral side surface 4. Thebonded magnet portion 1 is sufficiently thicker in the center portion 1b than in the end 1 a, such that it is thick in a magnetizationdirection to provide a sufficient magnetic force. The rotor has arotation shaft 3 tightly bonded to the soft magnetic portion 2 atcenter. The exposure ratio of the end surface 1 c is preferably 2% orless.

FIG. 1( b) shows a tensile stress distribution in the rotor of FIG. 1(a) when it was deformed. It should be noted that displacement isexaggerated to 2000 times in any figures showing a stress distribution.As is clear from FIG. 1( b), the largest stress is applied to theexposed end surfaces 1 c of the magnets. The bonded magnet portions 1are preferably arranged in the rotor such that the rotor has magneticpoles in even numbers of 4-12. It is preferable to circularly connectthe arcuate bonded magnet portions 1, to provide their end surfaces(magnetic pole surfaces) 1 c with a large area ratio, resulting in alarger amount of a magnetic flux and a larger reluctance effect.

FIG. 2( a) shows a permanent magnet-embedded rotor according to anotherembodiment of the present invention. The end surfaces 1 c of arcuatebonded magnet portions 1 are not exposed on a peripheral side surface 4,and the thinnest portions 2 a of a soft magnetic portion 2 between theend surface 1 c of the bonded magnet portions 1 and the peripheral sidesurface 4 are as thin as 0.3-1.5 mm. As shown in FIG. 2( b), the largesttensile stress is applied to the thinnest portions 2 a of the softmagnetic portion 2 in this rotor.

FIG. 3( a) shows a rotor comprising bonded magnet portions 1 each havinga rectangular cross section embedded in a soft magnetic portion 2 withgaps between their ends 1 a. FIG. 3( b) shows a tensile stressdistribution in the rotor of FIG. 3( a) when it was deformed. Thelargest tensile stress is applied to the thinnest portion 2 a of thesoft magnetic portion 2 between the ends 1 a of the bonded magnetportions 1 and the peripheral side surface 4.

FIG. 4( a) shows a rotor comprising fan-shaped bonded magnet portions 1embedded in a soft magnetic portion 2. Each bonded magnet portion 1 hasa cross section shape having a circular side along a peripheral sidesurface 4 of the rotor and a linear base. FIG. 4( b) shows a tensilestress distribution in the rotor of FIG. 4( a) when it was deformed. Asis clear from FIG. 4( b), the largest tensile stress is applied to thethin portion 2 a of the soft magnetic portion 2 between the bondedmagnet portion 1 and the peripheral side surface 4.

FIG. 5( a) shows a permanent magnet-embedded rotor according to a stillfurther embodiment of the present invention, in which each magnetic poleis formed by pluralities of bent bonded magnet portions 1A, 1B, and FIG.5( b) shows a permanent magnet-embedded rotor according to a stillfurther embodiment of the present invention, in which each magnetic poleis formed by pluralities of arcuate bonded magnet portions 1A, 1B, 1C.The rotor having laminar bonded magnet portions as shown in FIGS. 5( a)and 5(b) can generate a larger reluctance torque than the rotor havingsingle-layer, bonded magnets portion as shown in FIG. 1.

FIGS. 6( a)-6(e) show permanent magnet-embedded rotors according tostill further embodiments of the present invention. Each rotor comprisesthe thinnest portions 2 a of the soft magnetic portion 2 between bondedmagnet portions 1 and a peripheral side surface 4 of the rotor. Thereference numeral 37 in FIG. 6( c) denotes holes, and the referencenumeral 2 b in FIG. 6( d) denotes non-magnetic bodies.

FIGS. 7( a) and 7(b) show permanent magnet-embedded rotors according tostill further embodiment of the present invention. Each rotor comprisesthe thinnest portions 2 a of the soft magnetic portion 2 between bondedmagnet portions 1 and a peripheral side surface 4 of the rotor. Thereference numeral 2 b denotes non-magnetic bodies.

(2) Exposure Ratio of End Surfaces of Bonded Magnet Portions

When compression molding is conducted under as high pressure as about500-1000 MPa, cracking occurs vigorously by springback. This is due tothe fact that expansion by the springback is about 0.3% in the softmagnetic portion, while it is differently about 0.9% in the bondedmagnet portions, providing the resultant rotor with residual stress.Because the soft magnetic portion has a tensile strength of about 50MPa, while the bonded magnet portions have as small a tensile strengthas about 25 MPa, cracking occurs in the bonded magnet portions. As aresult of detailed investigations to reduce the residual stress underthe desired level, it has been found that in the case of a rotor inwhich the end surfaces of bonded magnet portions are exposed to aperipheral side surface of the rotor, cracking can be prevented when thewidth of each exposed end surface is 2% or less of the entire peripheryof the rotor. It has also been found that this ratio is substantiallyconstant regardless of the shapes of the bonded magnet portions. In thegraph of FIG. 11 showing the relation between a residual stress and theexposure ratio of end surfaces, for instance, the residual stress wouldchange as slightly as almost by the thickness of one curve even if thebonded magnet portions were provided with different shapes. This is dueto the fact that a stress is concentrated near the peripheral surface ofthe rotor. Accordingly, cracking can be suppressed by reducing theresidual stress on the peripheral surface of the rotor.

(3) Thinnest Portion of Soft Magnetic Portion

In the case of a rotor having bonded magnet portions completely embeddedtherein, the thinnest portions of a soft magnetic portion between thebonded magnet portions and a peripheral side surface of the rotor arepreferably as thick as 0.3-1.5 mm. When the thinnest portions arethinner than 0.3 mm, molding is difficult, and a residual stress isconcentrated in the thinnest portions, resulting in cracking in therotor. On the other hand, when the thinnest portions are thicker than1.5 mm, a magnetic flux is shorted-circuited in the thinnest portions,providing the rotor with lowered magnetic characteristics. It has beenfound that the preferred thickness of the thinnest portions issubstantially independent of the shapes of the bonded magnet portions.The outer diameter of the rotor is preferably about 15-150 mm forpractical applications.

(4) Density

A rotor compression-molded at as high pressure as 500-1000 MPa has adensity of 5.5-6.0 Mg/m³ in the bonded R-T-B magnet portion, 5.4-6.0Mg/m³ in the bonded R-T-N magnet portion, and 6.0-6.5 Mg/m³ in the softmagnetic Fe powder portion, for instance.

[2] Production Method

The permanent magnet-embedded rotor of the present invention can beproduced by the following three methods.

(1) A method comprising placing a preliminarily molded body of magnetpowder and a thermosetting binder in a die, charging a compound mainlycomposed of a soft magnetic powder and a thermosetting binder into thedie to carry out preliminary molding, applying higher pressure than thepreliminary molding pressure to them to make them integral, and finallycuring the thermosetting binder.(2) A method comprising forming a preliminarily molded body of magnetpowder and a thermosetting binder and a preliminarily molded body ofsoft magnetic powder and a thermosetting binder separately, placing bothpreliminary molded bodies in combination in a die, applying higherpressure than the preliminary molding pressure to them to make themintegral, and finally curing the thermosetting binder.(3) A method comprising placing a preliminarily molded body of softmagnetic powder and a thermosetting in a die, charging a compound mainlycomposed of a soft magnetic powder and a thermosetting binder into thedie to carry out preliminary molding, applying higher pressure than thepreliminary molding pressure to them to make them integral, and finallycuring the thermosetting binder.

Among them, the method (1) is most preferable because of high adhesionof the bonded magnet portion to the soft magnetic portion. Thus, takingthe method (1) for example, the production method of the presentinvention will be explained in detail. It should e noted, however, thatthis explanation will be applied to the methods (2) and (3) withoutmodifications as long as there is no contradiction.

[A] Production of Compound

A compound (magnet powder compound) mainly composed of magnet powder(particularly rare earth magnet powder) and a binder, and a compound(soft magnetic powder compound) mainly composed of soft magnetic powderand a binder are prepared. An anti-oxidant and a lubricant may be addedto each compound. A stabilizer, a molding aid, etc. may also be added tothe compound.

The anti-oxidant prevents the oxidation of the magnet powder and thesoft magnetic powder, preventing these powders from having deterioratedmagnetic characteristics, and improving the thermal stability of thecompounds to blending and molding, thereby enabling them to keep goodmoldability even with a small amount of the binder. Usable as theanti-oxidant are, for instance, tocopherols, amine compounds, amino acidcompounds, nitro-carboxylic acids, hydrazine compounds, cyano compounds,chelating agents such as sulfides capable of forming chelates with metalions, particularly Fe, etc.

The lubricant improves the flowability of the compound during blendingand molding, thereby making it possible to keep good moldability evenwith a small amount of the binder. Usable as the lubricant are aliphaticacids such as stearic acid or their metal salts, silicone oils, variouswaxes, etc.

[B] Compression-Molding Apparatus

Taking the rotor shown in FIG. 1( a) for example, an apparatus forcompression-molding the rotor of the present invention will be explainedreferring to FIGS. 8( a)-8(c). The compression-molding apparatus 10 is aso-called double-acting press comprising a die 11, which comprises upperand lower punches 13, 13′ for compression-molding bonded magnet portions1, upper and lower punches 14, 14′ for compression-molding a softmagnetic portion 2, and a core pin 15 for forming an opening in thecenter of the molded body.

FIG. 8( b) shows an assembly 16 of the upper punches 13, 14, and FIG. 8(c) shows upper punches 13 for molding the bonded magnet portions 1 andan upper punch 14 for molding the soft magnetic portion 2 in theassembly 16. An assembly (not shown) of lower punches 13′, 14′ hasbasically the same structure as that of the upper punch assembly 16. Thecompression-molding apparatus 10 is adapted for four bonded magnetportions 1, comprising four upper punches 13 and four lower punches 13′.The upper punch 14 has a cylindrical shape having four openings 14 acorresponding to the upper punches 13.

It is possible to prevent the rotor from being cracked by springback, byproviding a die cavity in its upper portion with a taper for suppressingdrastic springback, by reducing friction resistance by decreasing thesurface roughness of the cavity, or by reducing friction resistance by alubricant, etc.

[C] Compression-Molding Method

(1) Method (1)

The production of the rotor by the above method (1) using thecompression-molding apparatus 10 shown in FIG. 8 is conducted by theflowing steps as shown in FIG. 9.

(a) Step (a)

The lower punches 13′ are lowered to provide cavities for molding bondedmagnet portions, into which a magnet powder compound 17 mainly composedof 100 parts by mass of magnet powder having an average particle size of50-200 μm and 1-5 parts by mass of a thermosetting resin binder issupplied.

(b) Step (b)

The upper punches 13 are lowered to conduct the preliminary molding ofthe magnet powder compound 17 at a pressure of 200 MPa, for instance, toform a thicker bonded magnet portion 1 than the target thickness of therotor.

(c) Step (c)

The lower punches 14′ are lowered to the height of the lower punches 13′to provide a cavity for molding a soft magnetic portion 2, into which asoft magnetic powder compound 18 mainly composed of 100 parts by mass ofsoft magnetic powder having an average particle size of 1-50 μm and0.3-2 parts by mass of a thermosetting resin binder.

(d) Step (d)

The upper punches 14 are lowered to the height of the upper punches 13to conduct the preliminary molding of the soft magnetic powder compound18, to form the soft magnetic portion 2. This preliminary moldingadheres the soft magnetic portion 2 to the bonded magnet portion 1.

(e) Step (e)

The upper punches 13 and 14 are further lowered to integrally mold thebonded magnet portion 1 and the soft magnetic portion 2 at a higherpressure (for instance, 1000 MPa) than the preliminary molding pressure.With a slight step provided between the upper punches 13, 14 and thelower punches 13′, 14′ for the difference in springback between thebonded magnet portions 1 and the soft magnetic portion 2, they canfinally be provided with the same thickness. In the case of using ananisotropic magnet powder, a magnetic field is applied at least duringmolding.

When a thermosetting resin such as epoxy resins is used as a binder, thepreliminary molding of the magnet powder compound 17 and the softmagnetic powder compound 18 can be conducted at room temperature. Toincrease a filling density, however, it may be heated to about 120° C.

After elevating the upper punches 13, 14, the lower punches 13′, 14′ areelevated to take the resultant molded body out of the molding apparatus10. The resultant molded body is heat-cured at a temperature of 250° C.or lower. The molded body is integrally provided with a rotation shaft3, and magnetized to obtain a rotor integrally comprising permanentmagnets and a yoke.

This compression-molding method supplying the magnet powder compound 17and the soft magnetic powder compound 18 to a single apparatus toconduct preliminary molding and main molding successively can produce apermanent magnet-embedded rotor having bonded magnet portions 1completely embedded in a soft magnetic portion 2 at a low cost, withoutneeding bonding and assembling steps.

By conducting the preliminary molding and the main molding separately,the press-bonding strength of the bonded magnet portions 1 to the softmagnetic portion 2 can be increased. Particularly in the case of usingthe method (1) comprising preliminarily molding a magnet powder compoundcomprising magnet powder having a large particle size and then charginga soft magnetic powder compound comprising soft magnetic powder having asmall particle size into the die, part of the soft magnetic powderpenetrates into the bonded magnet portions 1, resulting in a rotorhaving a high press-bonding strength between the bonded magnet portions1 and the soft magnetic portion 2. On the contrary, a conventional rotorcomprising magnets bonded by an adhesive to the soft magnetic portionhas uneven thickness in bonding layers, and uneven bonding strength dueto rough bonding surfaces, resulting in low accuracy in the position ofthe magnet, and difficulty in obtaining stable bonding strength. Somerotors having specifications of providing a bonding strength of 10 MPaor more actually do not have a bonding strength of 5 MPa or more. On theother hand, rotors obtained by the method of the present invention havea press-bonding strength of 10 MPa or more, further 15 MPa or more interms of a shear stress between the bonded magnet portions 1 and thesoft magnetic portion 2.

(2) Method (2)

It comprises preliminarily molding bonded magnet portions from a magnetpowder compound mainly composed of magnet powder having an averageparticle size of 50-200 μm and a thermosetting resin binder, and a softmagnetic portion from a soft magnetic powder compound mainly composed ofsoft magnetic powder having an average particle size of 1-50 μm and athermosetting resin binder separately, assembling the bonded magnetportions and the soft magnetic portion in a die, making them integral ata higher pressure than the preliminary molding pressure, and finallythermosetting the resin. The molding time is drastically shortened inthis method because of no need to operate core pins in a complicatedmanner. Rotors obtained by this method have a press-bonding strength of5 MPa or more, further 5.5 MPa or more in terms of shear stress betweenthe bonded magnet portions and the soft magnetic portion.

(3) Method (3)

After the preliminary molding of a soft magnetic powder compound, amagnet powder compound is supplied. Though rotors obtained by thismethod have low press-bonding strength between the bonded magnetportions and the soft magnetic portion, there is no need to hold apreliminarily molded body in the cavity. Accordingly, this method iseffective to form extremely thin bonded magnet portions. In addition,with a rotation shaft placed in a cavity, it is possible to produce arotor comprising a rotation shaft integrally fixed by onecompression-molding operation.

In the above production method, rotors having a reduced eddy currentloss because of high electric resistance can be obtained, by providingpluralities of cavities for a magnet powder compound in radialdirections in a die such that each magnetic pole is formed by eachbonded magnet portion, and by supplying a low-electric-conductivity softmagnetic powder compound around them. In the conventional method,pluralities of coated magnets are assembled by bonding to form eachmagnetic pole, thereby reducing an eddy current loss. Accordingly, ithas many steps, resulting in a high production cost. On the contrary,because the method of the present invention can produce a rotor with thebonded magnet portions integral with the soft magnetic portion, it has afew steps and a low production cost. The larger a motor is, the morecurrent flows through permanent magnets, resulting in an increased eddycurrent loss. Accordingly, the method of the present invention isparticularly suitable for producing rotors for large motors.

The present invention will be explained in further detail referring toExamples below, without intension of restricting the present inventionthereto.

Example 1, Comparative Example 1

To suppress the generation of cracking in a rotor by springback, theshapes of the rotor and bonded magnet portions were modified. The rotorof Comparative Example 1 shown in FIG. 10( a), which is likely to becracked, has a cross section shape comprising bonded magnet portions 1and a soft magnetic portion 2, and the bonded magnet portions 1 havesides curved toward a center of the rotor, which are connectedcircularly. The connecting ends of the bonded magnet portions 1 areexposed on a peripheral side surface of the rotor.

100 parts by mass of magnet powder was mixed with 3 parts by mass of anepoxy resin (binder) to prepare a magnet powder compound, and 100 partsby mass of soft magnetic powder was mixed with 1.1 parts by mass of anepoxy resin to prepare a soft magnetic powder compound. 0.3 parts bymass of calcium stearate as a lubricant was added to 100 parts by massof each powder.

The resultant rotor had an outer diameter of 50 mm and an axial lengthof 100 mm, with the bonded magnet portions 1 as thick as 5 mm. Thebonded magnet portions 1 had wide exposed end surfaces, a width ratio(exposure ratio) of each exposed end surface 1 c to the entire peripheryof the rotor being 3.8%. FIG. 8( b) shows a tensile stress distributionof the rotor of FIG. 8( a) when it was deformed. The largest tensilestress was applied to the exposed end surfaces 1 c of the bonded magnetportions 1, where the tensile stress was 200 MPa.

Separately designed was a rotor of Example 1 comprising arcuate bondedmagnet portions 1, whose center portions were thickest as 5 mm, and endswere thinnest as 1 mm, embedded in a soft magnetic portion 2, such thatthe ends 1 a, 1 a of adjacent bonded magnet portions 1, 1 were separatefrom each other to prevent the short-circuiting of a magnetic fluxbetween magnetic poles, each end surface 1 c being exposed on aperipheral side surface 4, as shown in FIG. 1( a). The exposure ratio ofeach exposed end surface 1 c of the bonded magnet portions 1 was 0.6%.As shown in FIG. 1( b), the largest tensile stress was applied to theexposed end surfaces 1 c of the bonded magnet portions 1, where thetensile stress was 2 MPa.

FIG. 11 shows the relation between an exposure ratio and the maximumresidual stress on an exposed end surface. Because the soft magneticportion 2 has a tensile strength of about 25 MPa, it has been found thatthe exposure ratio should be 2% or less in such a design that theresidual stress is about 20 MPa or less.

Comparative Example 2

As shown in FIG. 12, a rotor comprising bonded magnet portions 1 andsoft magnetic portions 2, with notches 7 at the ends of the bondedmagnet portions 1. The rotor had an outer diameter of 50 mm, and eachbonded magnet portion 1 had a thickness of 5 mm. Each bonded magnetportion 1 had a rectangular cross section, with each end surface 1 cexposed to the notch 7. The exposure ratio of each end surface 1 c ofthe bonded magnet portion 1 was 3.5%. The exposure ratio of each endsurface 1 c of the bonded magnet portion 1 was a ratio of the length ofeach exposed surface 1 c to the total length of the peripheral sidesurface including the length of the notches 7 in FIG. 12. In the shapeshown in FIG. 12, the largest tensile stress was applied to the exposedend surfaces 1 c of the bonded magnet portions 1, where the tensilestress was 183 MPa.

It was found by analysis that this rotor met substantially the samerelation between the exposure ratio and the maximum residual stress atexposed end surfaces as shown in FIG. 11, despite slight difference. Thesame stress analysis was conducted with changed thickness of the centerand end portions of the bonded magnet portions 1, resulting in the sameresults.

Example 2

In a rotor shown in FIG. 2( a), in which the end surfaces 1 c of bondedmagnet portions 1 were not exposed to a peripheral side surface 4, thethinnest portions 2 a of the soft magnetic portion 2 between the endsurfaces 1 c of the bonded magnet portions 1 and the peripheral sidesurface 4 being as thin as 0.3 mm, a tensile stress was 19 MPa in thethinnest portions 2 a, to which the largest tensile stress was applied.Though it was expected that a residual stress were relaxed in the rotorof Comparative Examples 1 and 2 shown in FIGS. 10 and 12, in which thesoft magnetic portion 2 was divided by the bonded magnet portions 1 toinner and outer portions, outer soft magnetic portions 2 being freelyexpandable, it was found that cracking was actually suppressed more inthe rotor having the shape shown in FIG. 2( a).

FIG. 13 shows the relation between the thickness of the thinnest portion2 a and a maximum residual stress in that portion. In a rotor designhaving a residual stress of about 20 MPa or less because a soft magneticportion 2 has a tensile strength of about 25 MPa, the thinnest portion 2a should be as thick as 0.3 mm or more. However, when the thinnestportion 2 a is thicker than 1.5 mm, there is extreme short-circuiting ofa magnetic flux in the thinnest portions 2 a. Accordingly, the thinnestportion 2 a should be 1.5 mm or less.

Example 3

FIG. 3( a) shows a rotor comprising bonded magnet portions 1 each havinga rectangular cross section embedded in a soft magnetic portion 2 withgaps between their ends 1 a, 1 a. The rotor had an outer diameter of 50mm, and each bonded magnet portion 1 had a thickness of 5 mm, and atransverse width of 25 mm. The thinnest portions 2 a of the softmagnetic portion 2 had a thickness of 1.3 mm. FIG. 3( b) shows a tensilestress distribution in the rotor shown in FIG. 3( a) when it wasdeformed. The largest tensile stress was applied to the thinnestportions 2 a of the yoke, where the tensile stress was 11 MPa.

It was found by analysis that this rotor had substantially the samerelation between the thickness of the thinnest portions 2 a and themaximum residual stress in the thinnest portions 2 a as shown in FIG.13, despite slight difference. Stress analysis with changed thickness ofthe bonded magnet portions provided the same results.

Example 4

FIG. 4( a) shows a rotor comprising bonded magnet portions 1 totallyembedded in a soft magnetic portion 2, each bonded magnet portion 1having a cross section shape having an arcuate side extending along aperiphery of the rotor and a linear bottom. The rotor had an outerdiameter of 50 mm, and the bonded magnet portion 1 had the maximum widthof 7 mm, and a bottom length of 35 mm. The soft magnetic portion 2 had athin portion 2 a having a thickness of 1 mm outside the bonded magnetportions 1. FIG. 4( b) shows a tensile stress distribution in the rotorof FIG. 4( a) when it was deformed. The largest tensile stress wasapplied to the thin portion 2 a of the soft magnetic portion 2, wherethe tensile stress was 11 MPa.

It was by analysis found that this rotor had substantially the samerelation between the thickness of the thin portion 2 a and the maximumresidual stress therein as shown in FIG. 13, despite slight difference.Stress analysis with changed thickness of the bonded magnet portionsprovided the same results.

As shown in Table 1, the comparison of the rotors of Examples 1-4revealed that the highest motor output was obtained in Example 1 despitesubstantially the same area ratio of the bonded magnet portions to therotor (measured on a transverse cross-sectional view). It is thus clearthat the rotor of Example 1 had the best structure.

TABLE 1 Maximum Output of Area Ratio of Bonded No. Motor (kW) MagnetPortions (%) Example 1 2.4 29.5 Example 2 2.3 31.8 Example 3 2.1 29.3Example 4 2.2 32.8

Example 5

Using Nd—Fe—B magnet powder having an average particle size of 96.9 μm(measured by HEROS RODOS available from Sympatec), pure iron powderhaving an average particle size of 31.2 μm, an epoxy resin (binder), andcalcium stearate (lubricant), rotors having the same shape shown in FIG.1( a) were produced by the following three methods (a)-(c). A magnetpowder compound was obtained by adding 3 parts by mass of an epoxy resinand 0.5 parts by mass of calcium stearate to 100 parts by mass of themagnet powder. A soft magnetic powder compound was obtained by adding1.1 parts by mass of an epoxy resin and 0.5 parts by mass of calciumstearate to 100 parts by mass of the soft magnetic powder. A preliminarymolding pressure was 200 MPa, and a preliminary molding temperature wasroom temperature. Integrally molding pressure was 1000 MPa. Curing wasconducted at 170° C. for 2 hours, and the cured product was cooled toroom temperature over 30 minutes.

(a) A method comprising disposing a preliminarily molded body of themagnet powder and the binder in a die, supplying a compound mainlycomposed of the soft magnetic powder and the binder into the die forpreliminary molding, applying a higher pressure than the preliminarymolding pressure to make them integral, and finally curing theintegrated body.(b) A method comprising separately forming a preliminarily molded bodyof the magnet powder and the binder and a preliminarily molded body ofthe soft magnetic powder and the binder, assembling these preliminarilymolded bodies in a die, applying a higher pressure than the preliminarymolding pressure to make them integral, and finally curing theintegrated body.(c) A method comprising disposing a preliminarily molded body of thesoft magnetic powder and the binder in a die, supplying a compoundmainly composed of the magnet powder and the binder into the die forpreliminary molding, applying a higher pressure than the preliminarymolding pressure to make them integral, and finally curing theintegrated body.

The bonded magnet portion and the soft magnetic portion were partiallycut out of each of the resultant rotors to evaluate their magneticproperties. The bonded magnet portion had Br≧0.6 T and Hcj≧700 kA/m, andthe soft magnetic portion had Bm≧1.4 T and Hc≦800 A/m. As thepress-bonding strength between the bonded magnet portions and the softmagnetic portion, a tensile strength at an interface between the bondedmagnet portion and the soft magnetic portion was measured using a smalltest piece according to JIS-K7113. The results are shown in Table 2.

TABLE 2 Compression Tensile Strength Molding Method (MPa) (a) 15.2 (b)5.7 (c) 5.5

Example 6

FIG. 14 shows a rotating machine comprising the permanentmagnet-embedded rotor of Example 1. The rotor was surrounded by a softmagnetic material having electric conductivity of 20 kS/m or less. Inthe figure, A₂ denotes a magnetic circuit generating a magnet torque,and A₃ denotes a magnetic circuit generating a reluctance torque.

Using a magnet powder compound comprising 100 parts by weight ofisotropic Nd—Fe—B magnet powder and 2 parts by weight of an epoxy resin,and a soft magnetic powder compound comprising 100 parts by weight ofinsulation-coated pure iron powder and 2 parts by weight of an epoxyresin, a rotor was produced by the method shown in FIG. 9 under theconditions of a preliminary molding pressure of 200 MPa and a mainmolding pressure of 1000 MPa. Curing was conducted at 170° C. for 2hours, and the cured product was cooled to room temperature over 30minutes. A rotation shaft was mounted to the resultant permanentmagnet-embedded rotor, and the bonded magnet portions were magnetizedsubstantially in their thickness directions.

With the above rotor combined with a stator having six slots and aY-connected winding, a 120-degree rectangular wave current was suppliedto the winding to measure a rotation torque. The ampere-turn number ineach slot was 300 AT. The bonded magnet portions were partially cut outto evaluate their magnetic properties, which were Br≧0.6 T, and Hcj≧700kA/m. Also, the soft magnetic portion was partially cut out to evaluateits magnetic properties, which were Bm≧1.4 T, and Hc≦800 A/m.

A torque generated by this rotating machine was measured. The relationbetween an electrical angle and a normalized torque is shown in FIG. 15.When a usual permanent magnet rotor is used, torque-generating centerangles are 90° and 270° as electrical angles, because a rotation torqueis generated by a magnetic field generated by permanent magnets, whichcrosses stator coils. It has been found, however, that themaximum-torque-generating center angles move to substantially 100° and280° in the rotor of the present invention, because it generates areluctance torque, too.

EFFECT OF THE INVENTION

As described above, because the permanent magnet-embedded rotor of thepresent invention has a structure, in which bonded magnet portionscomposed of magnet powder and a binder are embedded in a soft magneticportion composed of soft magnetic powder and a binder, the magnetic polesurfaces of the bonded magnet portions being substantially embedded inthe soft magnetic portion, it has the advantages that (a) there are nogaps acting as magnetic resistance between the bonded magnet portionsand the soft magnetic portion, so that a magnetic flux can be utilizedefficiently; (b) high dimensional accuracy is achieved even in thinportions between the bonded magnet portions and a peripheral sidesurface; (c) a reluctance torque is effectively used; and (d) the numberof assembling steps can be reduced. In addition, cracking due tospringback can be prevented by forming the bonded magnet portions indesired shapes, or by setting the width of each exposed end surface ofthe bonded magnet portions at 2% or less of the entire periphery of therotor. Further, a press-bonding strength between the bonded magnetportions and the soft magnetic portion can be increased by desirablyrestricting the particle sizes of the magnet powder and the softmagnetic powder.

The production method of the present invention enjoys a high degree offreedom in the shapes of the bonded magnet portions. Though theconventional rotor having magnets bonded by an adhesive has unnecessarygaps between a yoke and the magnets, the present invention provides ahigh-performance, permanent magnet-embedded rotor without gaps betweenthem using a small amount of a resin and a small number of steps,because bonded magnet portions and a soft magnetic portion areintegrally compression-molded. In addition, it is possible to preventthe short-circuiting of a magnetic flux generated by the bonded magnetportions in yoke portions between magnetic poles, thereby enabling theeffective use of the magnetic flux from bonded magnet portions.

1. A method for producing a rotor comprising bonded magnet portions anda soft magnetic portion, the method comprising, in the order mentioned,(a) preliminarily molding steps consisting of compressing a magnetpowder compound mainly composed of magnet powder and a binder to moldsaid bonded magnet portions; charging a soft magnetic powder compoundmainly composed of soft magnetic powder and a binder, such that saidsoft magnetic portion is in contact with said bonded magnet portions,and compressing said soft magnetic powder compound to mold said softmagnetic portion; and (b) simultaneously compressing said bonded magnetportions and said soft magnetic portion to make said bonded magnetportions and said soft magnetic portion integral.
 2. The method forproducing a rotor according to claim 1, wherein a thermosetting resin isused as said binder, and wherein a thermosetting treatment is conductedafter said bonded magnet portions and said soft magnetic portion aremade integral.
 3. A method for producing a rotor comprising bondedmagnet portions and a soft magnetic portion, the method comprising (1)preliminarily molding steps consisting of compressing (a) a magnetpowder compound mainly composed of magnet powder and a binder to moldsaid bonded magnet portions, and (b) a soft magnetic powder compoundmainly composed of soft magnetic powder and a binder to mold said softmagnetic portion separately; assembling said bonded magnet portions andsaid soft magnetic portion; and (2) simultaneously compressing saidbonded magnet portions and said soft magnetic portion to make saidbonded magnet portions and said soft magnetic portion integral.
 4. Themethod for producing a rotor according to claim 3, wherein athermosetting resin is used as said binder, and wherein a thermosettingtreatment is conducted after said bonded magnet portions and said softmagnetic portion are made integral.
 5. A method for producing a rotorcomprising bonded magnet portions and a soft magnetic portion, themethod comprising, in the order mentioned, (a) preliminarily moldingsteps consisting of compressing a soft magnetic powder compound mainlycomposed of soft magnetic powder and a binder to mold said soft magneticportion; charging a magnetic powder compound mainly composed of magnetpowder and a binder, such that said bonded magnet portions are incontact with said soft magnetic portion, and compressing said magnetpowder compound to mold said bonded magnet portions; and (b)simultaneously compressing said bonded magnet portions and said softmagnetic portion to make said bonded magnet portions and said softmagnetic portion integral.
 6. The method for producing a rotor accordingto claim 5, wherein a thermosetting resin is used as said binder, andwherein a thermosetting treatment is conducted after said bonded magnetportions and said soft magnetic portion are made integral.